Present catheter based optical probes (optrodes) for continuous monitoring of various parameters in body fluids require separate sensors and fibers for each parameter measured, thus requiring large delivery devices. A small, inexpensive, disposable, and continuously monitoring multiparameter probe would be cost effective, present clinical information immediately, and provide diagnostics not presently available. The objective is to demonstrate the feasibility of a compound sensor optrode, in which multiple parameters (pH/pCO2/pO2) can be monitored by a single small optical fiber. The specific aims of Phase I are: 1. To build first a pCO2/pO2, and then an O2/pH sensor on a single optical fiber and then measure the effectiveness of the probe in body fluids with known O2/CO2 concentrations. 2. To devise a method for combining all three sensors on the same optical fiber. The longer term Phase II objective would be to build and characterize a single optical fiber multisensing probe that could fit inside a 22 gauge catheter, yet allow sufficient blood draw and blood pressure monitoring performance.